Key Vocabulary Terms:
Pressure: The amount of force per unit of area. Air pressure is a result of the force gravity on the atmosphere. Air Pressure is measured by an instrument called a barometer. Air Pressure at sea level is about 15 pounds per square inch.
Pressure is influenced by the density of the air. The higher the density, the greater the pressure.

Temperature: the measure of the speed of the molecules of a substance. The higher the temp of the air, the faster molecules move and the farther they are apart. (the lower the density and the lower the pressure they have)

Density: This term describes the amount of mass per unit of volume. The greater the density of an object, the more mass it has in a certain space. Density is affected by temperature. Increase the temperature, you decrease the density of the object, because its molecules are moving faster, and thus become more spread out over a unit of volume. Think of the hot air balloon example: As the air is heated in the balloon it’s temperature increases and the air molecules become more spread out=thus inflating the balloon.
Air masses have different densities: Cooler air masses have greater density because they have more air molecules in he same area of volume than a Warmer air mass. Because of their different densities they have different pressures.

COOL DRY AIR MASS=HIGH DENSITY=HIGH PRESSURE
WARM AND WET AIR MASS=LOW DENSITY=LOW PRESSURE

Humidity: the amount of water vapor in a certain volume of air.

Atmospheric Energy:
The earth receives approximately 2 billionths (.000000002) of the sun's energy. Of this-
33% of solar energy reflected back to space
20% absorbed by the air
47% reaches the surface.
The atm acts like a blanket and transfers heat globally. It does not allow the earth to overheat or to cool down to much. It dissipates solar energy fromt the equator to the poles.

Solar Energy is in three forms of radiant energy. They are visible light, infrared light (heat), and ultraviolet light. These forms of electromagnetic waves are different in wavelength. Ultraviolet has the shortest wavelength and is the most powerful. Infrared has the longest.
Gases in the atmosphere scatter the blue light ( visible light) and thus gives the "sky" a blue color. The more water vapor in the atmosphere the grayer the sky appears.

Greenhouse Effect:The earth's surface absorbs short wave radiation and reradiates it as longer wave radiation which is prevented from leaving the earth by the clouds. This raises the earth's overall temperature. This is the same thing that happens in a nursery greenhouse. It can be quite cold outside but very warm inside the greenhouse.

Water plays an important role in the temperature of air. Water absorbs or loses heat very slowly. During the day land heats up faster than water. So the air above the land heats up faster than the air above the water. At night, land cools faster than water and so does the air above it.

The Earth's Shape : is important in heating the earth-more direct sunlight on the equator=more heat. Since the air above the equator is the warmest it also less dense than the colder air over the poles.

So the air over the poles is denser than equatorial air. This difference is air densities sets up CONVECTION CURRENTS.
These convection currents flow from the poles to the equator and back again. Cold air from the poles sinks, travels down to the equator, forces the warm equatorial air to rise, and travels to the poles where it cools and sinks.

WINDS: are almost always caused by pressure differences in the atmosphere. Pressure differences are caused by different air temperatures. Warm air is less dense so it has less pressure. Cold air more dense so it has higher pressure.

Convection cells are complete circle of moving air caused by temperature differences movement of air in convection cells causes winds along the ground to flow from areas of high pressure to low pressure.

WIND PATTERNS that cover the entire earth are again caused by unequal heating of the earth's surface. The result is colder high pressure air at the poles and warmer low pressure air at the equator.
The second factor that affects wind patterns in the fact that the earth is rotating on its axis. (If it was stationary we would have only 2 convection cells. One from the north pole to the equator and one from the south pole to equator.)This difference in speed of rotation causes the coriolis effect.
Air moving in the northern hemisphere appears to move to the right when traveling north or south. In the southern hemisphere it is the opposite. Air appears to move to the left.

Water enters the air by the process of evaporation.The ocean surface is where most water vapor enters the atmosphere.

Air at a particular temperature can only hold a certain amount of water vapor=at a certain temperature there is only enough space for the water vapor molecules to fit. The warmer the air the more water molecules it can hold. Air that holds all the water it can is said to be saturated.
Why? Temperature is the key. The warmer the air the faster the movement of air molecules; thus the more space between them for molecules of water vapor.

Relative humidity=how much water vapor in the air compared to how much it could hold
DEW POINT=The temperature at which the air becomes saturated with water vapor--Cooling the air lowers the amount of water vapor air can hold. It decreases its saturation point.
Dew points differ depending on the humidity of the air before the temperature started dropping

If the air is cooled beyond its dew point =condensation-will occur
When the dew point is below the freezing pt-frost occurs.

WEATHER:
Clouds: Formation and types:
Condensation- two things are necessary-lowering of the temp and a suface to form on.
There are 3 ways in which air mass can be cooled. One, it can touch a cold surface. Two, it can mix with cold air mass. Three, the air mass can expand. Expansion of any gas will lower the temperature of that gas.

There are 2 ways in which air masses are lifted. 1. Travely over mountains 2. By a colder air mass
When an air mass rises, it is cooled by expansion. The water vapor molecules are squeezed out of the air (condensation) and condense on the solid particles in the air. As these water droplets get larger and larger they begin to reflect light. This reflection of white light gives us clouds.

Clouds are classified by their shape and their height. The 3 basic shapes are Stratus, Cumulus, and Cirrus. Clouds can be a combination of 2 shapes.

Clouds below 7 kilometers are called alto while those above 7 k are called cirro.

Cumulus clouds have vertical development. They are produced by rapidly rising air, that is cooled quickly and condenses out as large pillow like shapes.

The term Nimbus is given to stratus or cumulus clouds that produce rain or snow.

PRECIPITATION:FORMATION. There are 2 ways in which rain is formed. The first is by a process of coalescence. In this process smaller water droplets join together to form a raindrop. This raindrop is approximately a million times larger than the initial water droplets. When the raindrop attains enough mass it will began to fall. As it falls it adds more droplets to it.By the time it reaches the earth it has the typical raindrop size. This type of rain formation occurs mostly in the tropics.

In the higher latitudes another type of formation happens. This process is called supercooling. It is a process that involves the cooling of water below the freezing point. Because of the lack of freezing nuclei the water vapor ends up condensing on ice crystals. When the ice crystals gain enough mass they fall. Depending on the temperature they fall as either rain or snow.

Air Mass: A large body of air with uniform temperature and moisture content is called an air mass.-Air that remains over an area on the earth's surface for a time, will take on the characteristics of that area. Air over the ocean is wetter than air over land. Air over the equator is warmer and less dense than air over the poles (colder and more dense). An air mass forms when there is very little pressure differences, so the air remains stationary. This allows it time to take on the characteristic of the earth's surface.
Air masses can be thousands of kilometers in diameter. Air masses that form over the arctic regions are very cold and dry. Air masses that form over the tropical oceans are warm and moist.
Air masses are classified according to their source regions. The source region determines the temperature and humidity of the air mass.There are four main source regions: polar, tropical, maritime(ocean), and continental. These sources in combination produce the four main types of air masses: maritime polar (mP), maritime tropical (mT), continental polar (cP), and continental tropical (cT).

Three polar masses influence weather in North America. These masses are called polar Canadian, polar Pacific, and polar Atlantic.
Four tropical air masses influence the weather in North America. The Tropical continental, a cT air mass, forms only during the summer over Mexico and the southwestern US. It brings clear, dry, and very hot weather.

FRONTS: When two air masses meet, temperature differences usually keep the air masses separate. The air of a cool air mass is dense and does not mix with the less dense air of a warm air mass. Thus, a boundary, called a FRONT, usually forms between air masses. Fronts can vary in length from 100 km long to 1000 km long. Changes in weather usually take place along the various types of fronts.

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